Dewaxing lubricating oils



Jan. 22, 1935.

MIDCONTINE CYLINDER STOCK POUR TEST J CH/LLERS H. e. SMiTH DEWAXING LUBRICATING OILS Filed July 14, 1932 2 Sheetsfiheet l IVA PH THA CENTEIF'UGE iCLAY FILTERS} 'CHIL E IVHPHTHA L cans an.

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Jan. 22, 1935. H sMlTH 1,989,028

DEWAXING LUBRICATING OILS Filed July 14, 1932 2 Sheets-Sheet 2 RE F/NED Lus. DIST/L LATE P/mr- DEWAXED POUR TEST 35 F.

65 PTS- NA PHTHA GAS OIL LUB RIC ATING OIL CHILLERS COLD SETTL/NG P BOT TOMS CLAY FILTERS FIN/SHED OIL POUR TEST NEUTRAL OIL HAVING WAX HAZE Poul? T EST NA PHTHA LUBEICATING CHILLERS 001.0 SETTLING O lPEDl/WN6 TANK -30 F. 'lflLL WAX SETTLING B07- TOMS ig-0 ,5 CLAY FILTERS FINISHED .ou POUROTEST ZYWQ/YVM Herschel afiiwi/i'h,

x Emm Patented Jan. 22, 1935 UNITED STATES PATENT OFFICE DEWAXING LUBRICATING OILS poration of Texas Application July 14, 1932, Serial No. 622,552

11 Claims.

This invention relates to dewaxing lubricating oils; and it comprises a process wherein a lubricating stock of residual or overhead type, having a low wax content corresponding to a pour test of not substantially above 40 F., is diluted, usually with a light distillate, the resulting dewaxing stock is chilled and cold settled, the top oil from the settling step is drawn off and processed to recover a finished lubricant, the wax 1o settlings being then centrifuged for wax removal. advantageously at somewhat lower temperatures, and the oil thus recovered from the centrifuging step is either added to the top oil from the cold settling step or recycled, according to'whether or not its wax content is sufficiently low to permit finish processing; all as more fully hereinafter set forth and as claimed.

The dewaxing of lubricating oils has always represented an important problem in the petroleum industry. Recently the demand for viscous, low cold-test lubricants for the preparation of blended motor oils has greatly increased. The more viscous of these oils are known as bright stocks having viscosities ranging from about 60 to 210 seconds at 210 F. by the Saybolt Universal Viscosimeter (S. U. V.) and pour tests from +30 F. down to F. or lower. The demand for these lubricants has been met by the development of special methods for wax removal.

One of the early methods used for wax removal from viscous lubricating stocks was the so-called cold settling method. This method consists merely in diluting a lubricating stock with a light distillate such as naphtha, chilling the mixture to a low temperature and settling the wax over a period of several days. This method did not prove advantageous in the case of oils having a high wax content due to the low yield 40 of top oil from the settling step. It is for this reason that this method has been largely superseded by centrifugal and other special methods which tend to pack the wax in a more solid or compact form with a considerable saving in time. Two such methods are described and claimed in my copending applications, Serial No. 596,093, filed March 1, 1932 and Serial No. 610,200, filed May 9, 1932.

I have found, however, that certain advantages result from a combination of cold settling and packed state of the larger proportion of wax.

The resulting oil of relatively low wax content can then be advantageously cold settled with the production of an oil of lower pour test and having a clarity and brightness rarely if ever encountered in centrifugal dewaxing, other conditions being the same. Cold settling produces an oil having a pour test of from 5 to 15 F. lower than centrifugal dewaxing by means of a liquid separator at the same temperature. and hence, in the production of oils having extremely low pour tests, this method has an important advantage. Moreover, in oils of low initial wax content, the wax can be settled in comparatively small volume, the wax settlings being thereafter usually dewaxed by centrifugal force or other mechanical means to recover oil. The dewaxing 0f the wax settlings may, if desired, be accomplished in a separate centrifuging step, after which the oil can be (1) mixed with the top oil from the cold settling step, (2) finished separately or (3) returned to an earlier dewaxing step in case the wax'content is too high for the oil to be advantageously mixed with the top oil for finish processing. An alternative procedure is to return the wax settlings directly to the preliminary dewaxing step to be mixed with the diluted dewaxing stock before or after chilling. This procedure is advantageous when the wax content of these settlings is of about the same order of magnitude as the wax content of the mixture subjected to the primary centrifuging. The wax settlings need not be warmed up but can be added to the chilled dewaxing stock or, in the case of continuous chilling, to this stock during chilling at a stage which corresponds in temperature to that of the wax settlings.

The above method is especially adapted to the removal of a wax hazefrom stocks which are otherwise suitably dewaxed. Such stocks, according to my new method, are first chilled and cold settled. The top oil is then drawn off, usually in condition suitable for finish processing, and the wax settlings are then centrifuged by means of a liquid separator.

In' many cases an oil of the required pour point can be recovered from the wax settlings by chilling these settlings to temperatures of from 10 to 40 F. below those used in the cold settling step and then centrifuging at these lower temperatures. In this case the oil recovered from the dewaxingof the wax settlings may be added di-. rectly to the top oil from the cold settling step for finish processing.

My new method has several advantages over any simple or repeated method of centrifuging which can be employed for producing oils having the same pour test. As mentioned previously, for the same chilling temperatures, my method pro duces oils of lower pour point, usually from 5 to 15 lower. Less equipment is required. The required centrifuge capacity is reduced by one third or more; usually much more. In addition my method is suitable for dewaxing some stocks which cannot be dewaxed by centrifugal force due to the packing of the wax in hard layers in the centrifuge. While the removal of a slight wax haze, by centrifugal methods, is often as diflicult and expensive as the removal of larger quantities of wax, such removal by my new process can be conducted at a reduced cost. I therefore consider my method particularly adapted to the removal of these small quantities of wax.

My invention is illustrated and can be more readily explained by referring to the accompanying drawings in which the figures represent flow sheets of three illustrative embodiments of my invention, wherein certain dewaxing stocks are treated by a series of successive operations with the ultimate production of finished oils of low pour test. The several operations are indicated in the fiow sheets by appropriate legends. In this showing:

Fig. 1 illustrates a method particularly suitable for the dewaxing of heavy, paraffn type, lubricating stocks of the nature of mid-continent cylinder stocks or of heavy lubricating stocks derived from special crudes and containing only small amounts of wax;

Fig. 2 illustrates a method particularly adapted to the dewaxing of highly refined lubricating distillates or of light residuals of the naphthenic type, which have already been partially dewaxed; while Fig. 3 illustrates a process especially adapted for the removal of a wax haze from oils that are otherwise suitable as to wax content.

In the particular process represented by Fig. l, 35 parts of a mid-continent cylinder stock having a pour test of 100 F. were diluted with 65 parts of naphtha. This mixture, as shown on the chart, was run through chillers which reduced the temperature to about 10" F. and was then centrifuged. This step lowered the pour point to about 35 F. (If desired, the partially dewaxed stock can be clay filtered at this point.) The partially dewaxed oil was again sent through chillers at a lower" temperature. thereafter being led to a cold settling tank. In the latter tank the chilled product was maintained at a temperature of 35 F. for about 48 hours. During the first 36 hours of this period the tank was agitated every half hour. After the cold settling period the top oil was carefully drawn off without disturbance of the wax settlings. This top oil, after reduction and clay filtering, was found to have a pour point of 0 F.

The wax settlings from the cold settling step were centrifuged to remove as much wax as was possible and the oil recovered was sent back to the chillers operating at 35 F. As shown on the flow chart an optional method of procedure is to return the oil recovered from the centrifuges to the chillers operating at 10 F.

In using the above method the centrifuges or liquid separators in the preliminary dewaxing step can be operated at a capacity amounting to from 5 to 6 barrels per hour. This is about 50 per cent greater capacity than usual. These centrifuges are employed merely for removing the bulk of the wax. When operated in this manner a harder wax is obtained with less loss of oil than would occur if the oil was chilled to lower temperatures. The pour test of the oil is reduced by this procedure, the centrifuged oil having pour tests of from 20 to 35 F. Lower pour tests are often not required at this point. The top oil from the cold settling operation which follows usually amounts to from 60 to per cent of the total. Substantially all of the wax is thus concentrated in the 20 to 40 per cent of wax settlings. In order to conduct my process it is, of course, essential that these wax settlings be of the proper consistency to flow through a centrifuge at the low temperatures specified for dewaxing. These wax settlings do not resemble petrolatum which, as is well known, is a wax gel with which some oil is associated and which is incapable of being centrifuged. The wax settlings obtained in my process consist primarily of oil (diluted with naphtha) in which small particles of wax are suspended.

When paraflin type cylinder stocks are employed in the above process the wax settlings obtained are often too concentrated in wax to permit centrifugal dewaxing to a 0 F. pour point in a single operation. For this reason it is advisable to recycle the oil recovered from the wax settlings. However, the dewaxed oil obtained from the wax settlings may be reduced and filtered, if desired, to produce a finished oil having from 10 to 20 F. higher pour test than that obtained from the top oil. In Fig. 2 there is shown another illustrative embodiment of my invention. In this operation a highly refined lubricating distillate which had already been partially dewaxed by centrifugal or other mechanical means and having a pour point of about 35 F. was employed. This type of oil usually develops a wax haze on ageing. The oil was diluted with naphtha and chilled to a temperature of 10 F. The mixture was cold settled at this temperature for a period of 60 hours. The top oil was drawn off. The remaining wax settlings were chilled to 25 F. and centrifuged, the oil recovered being added to the top oil. This mixture was then reduced and filtered to recover a finished lubricating oil having a pour test of +10 F. and free from wax haze upon ageing.

An optional method of treating the wax settlings obtained above is illustrated by the dotted lines on the figure. Use is made of a filter aid such as fullers earth, Georgia clay or infusorial earth. This can be added to the oil either before the cold settling step or afterwards. It often promotes subsidence to some extent in the cold settling and, in such cases, I usually prefer to add it before this step. The filter aid may be added in an amount equaling about 0.3 pound per gallon of oil. After cold settling, the wax settlings, which contain any added filter aid are chilled, usually at a lower temperature than that employed in the cold settling step and then filtered. The recovered oil is then usually added to the top oil for finish processing or it may be processed separately or returned to the first chilling step to -10 F. shown on the flow chart (Fig. 2). This is advantageous if the oil contains too much wax to produce a satisfactory product. The added filter aid is removed from the oil with the wax cake.

The process shown in Fig. 2 is suitable for dewaxing highly refined lubricating distillates 0f the parafiin type which have been partially dewaxed; that is distillates having a pour point of not over 40 F. for example. It is applicable to some naphthenic type residual oils-or overheads which contain only a small wax content. It is also advantageous in dewaxing oils of low pour test, which have been highly refined with consequent removal of substances which inhibit the formation of wax gels. The usefulness of this process depends, of course, upon whether the wax settlings can be dewaxed by centrifugal force to an extent permitting the oil recovered therefrom to be added to the top oil. Otherwise the oil should be recycled, to be again cold settled, or finished separately to produce a lubricating oil of higher pour point.

In Fig. 3 there is shown a specific embodiment of a process suitable for removing a wax haze from oils. Such hazes are frequently encountered in oils of moderate pour test after a period of ageing. Such oils would otherwise not require a dewaxing step. They also tend to occur in oils subjected to treatment with aluminum chloride. Removal of such wax hazes by centrifuging is at times an expensive and not an altogether satisfactory method. In the process represented by the figure a neutral oil having a slight wax haze and a pour point of +10 F. was diluted with naphtha. This mixture was then chilled and cold settled at a temperature of 30 F. The wax settlings were chilled and centrifuged at a temperature of 40 F., the dewaxed oil being added to the top oil recovered from the cold settling step. The finished oil produced in this process had a pour point of F. and was free of wax haze upon ageing.

While the accompanying fiow charts represent what I consider the best embodiments of my invention, several modifications can be made in the processes there set out without departing from the scope of the present invention. In some cases I have found that the cold settling of the wax can be facilitated by the addition of small amounts of amorphous wax or oils containing the same to the dewaxing stock. It is also sometimes advantageous to add a coagulant such as isopropyl alcohol, glucose, sperm oil soaps, zinc stearate, ferric oleate, etc. These coagulants can be added in proportions varying from about 0.1 to 1.0 per cent by weight of the dewaxing stock. By the term coagulant I mean those substances which, when added in even extremely small proportions to a dewaxing stock, tend to inhibit the formation of a wax gel and to promote the agglomeration into fiocks of the colloidal wax particles. Varying proportions of naphtha or other diluent can be used in my dewaxing stocks. When producing viscous lubricating oils of extremely low pour test, such as 10 F. or below, it is usually advantageous to use as high as 75 parts of naphtha to 25 parts of oil in making up the dewaxing stock.

In the cold settling step rapid or shock chilling can be employed. In some instances, in fact, shock chilling appears to produce better results than slow chilling. This makes it feasible to employ a continuous process of cold settling. For this purpose settling tanks usually known as thickeners" can be employed. These are equipped with multiple trays and extremely slowmoving scrapers. It is usually advisable in using continuous methods to employ a diluent, such as pentane, providing a large differential in gravity between the wax settlings and the top oil. Otherwise the slightest disturbance of the settlings by the scrapers is likely to throw wax into the top oil.

If the usual batch settling tanks are employed for cold settling they are advantageously provided with a swing pipe having a funnel at the end which may be gradually lowered to draw off the top oil. If desired, a revolving horizontal perforated arm can be employed to draw off the wax settlings from the bottom, the perforations in the arm being directed downwards. Drawing off of cleartop mixture can usually be started within about 5 hours after completion of chilling. Extremely large settling tanks can be employed. Cone bottoms are best but are more expensive.

In any type of settling tank it is advisable, as a safety precaution against static electricity and other explosion or fire hazards to use an inert gas, such as nitrogen, over the oil and to provide breathers equipped with air or gas drying units. The cold settling tanks can be equipped with chilling coils if desired, the use of the usual chillers being dispensed with; or such coils can be employed merely for making up heat losses, for example where separate continuous chillers are used.

In some cases it is advisable to cold settle.

black; that is, before refining. The wax settlings and oil can then be refined separately. The black settlings, after refining, are usually difficult to centrifuge but can be modified by the addition of wax or residual oils in accordance with the methods outlined in my acknowledged copending applications.

Various diluents can be employed in the cold settling step. I usually employ close out light paramn-type naphtha distillates having a gravity ranging from 90 to about 56 A. P. I. The best of these distillates usually have a gravity lying between 70 and 60 A. P. I. However, there are a large number of other diluents which can be employed. These include pentane, hexane, and the like.

What I claim is:

l. The process of removing a wax haze from viscous lubricating stocks which comprises diluting a lubricating stock having a wax haze, cold settling the diluted stock, in such manner as to produce a low pour test supernatant oil free from a wax haze and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said Wax haze can be removed by centrifugal dewaxing; separating the bulk of said lubricating stock as low pour test top oil from said wax settlings, chilling the latter to a temperature somewhat lower than that employed in the cold settling step, dewaxing the chilled wax settlings including a substantial proportion of wax by centrifugal force by means of a liquid separator, uniting the oil thus recovered with'the top oil and processing the mixture to obtain a finished lubricant.

2. In the dewaxing of lubricating oils, the process which comprises dewaxing such an oil by centrifugal force by means of a liquid separator to the point at which its pour test is not substantially above 40 F., chilling and cold settling the partially dewaxed stock in such manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxing; removing the bulk of the lubricating oil as a low pour test top layer, chilling and centrifuging the wax settlings by means of a liquid separator at a temperature somewhat lower than that employed in the cold settling step and uniting the recovered oil with the top oil from the cold settling step.

3. In the dewaxing of lubricating oils, the process which comprises dewaxing such an oil by centrifugal force by means of a liquid separator to the point at which its pour test is not substantially above 40 F., chilling and cold settling the partially dewaxed stock in such manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxing; removing the bulk of the lubricating oil as a low pour test top layer, chilling and centrifuging the wax settlings by means of a liquid separator and recycling the recovered oil to the first centrifuging step.

4. In the dewaxing of lubricating oils, the process which comprises dewaxing such an oil by centrifugal force by means of a liquid separator to the point at which its pour test is not substantially above 40 F., chilling and cold settling the partially dewaxed stock in such manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxing; removing the bulk of the lubricating oil as a low pour test top layer, chilling and centrifuging the wax settlings by means of a liquid separator and recycling the recovered oil to the chilling step preceding cold settling.

5. In the dewaxing of lubricating oils, the process which comprises chilling and cold settling an oil having a pour test not substantially above 40 F. in such manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxing; removing the bulk of the lubricating oil as a low pour test top layer, dewaxing the wax settlings containing a substantial proportion of wax by centrifugal force by means of a liquid separator to recover an oil therefrom and finish processing the top oil and the oil recovered from the wax settlings.

6. The process of claim 5 in which the top oil and the oil recovered from the wax settlings are mixed before being finish processed.

'7. The process of claim 5 in which the wax settlings are centrifuged at a temperature of from 10 to 40 F. lower than that employed in the cold settling step.

8. In the dewaxing of lubricating oils, the process which comprises chilling and cold settling an oil having a pour test not substantially above 40 F. in such manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxing; removing the bulk of the lubricating oil as a low pour test top layer, dewaxing the wax settlings containing a substantial proportion of wax by centrifugal force by means of a liquid separator to recover an oil therefrom and recycling the oil recovered from the wax settlings to be again cold settled.

9. In the dewaxing of lubricating oils, the process which comprises dewaxing such an oil by centrifugal force to obtain a pour test not substantially above 40 F., again dewaxing by chilling and cold settling the oil insuch manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxing; separating the bulk of the lubricating oil as a low pour test top layer from the wax settlings containing a substantial proportion of wax, centrifuging the latter by means of a liquid separator and returning the oil thereby recovered to a former dewaxing step.

10. In the dewaxing of lubricating oils having a low wax content, the process which comprises adding a filter aid to such an oil, chilling and cold settling in such manner as to obtain a low pour test supernatant oil and wax settlings capable of being directly filtered; said cold settling being conducted at a temperature above that at which said low pour test oil, can be obtained by centrifugal dewaxing; separating the bulk of the lubricating oil as a low pour test top layer, from the wax settlings, filtering the latter and returning the oil thereby recovered to the process.

11. In the dewaxing of lubricating oils having a low wax content, the process'which comprises adding a small proportion of a coagulant to such an oil, chilling and cold settling coagulant to such an oil, chilling and cold settling in such manner as to produce a low pour test supernatant oil and wax settlings capable of being directly centrifuged; said cold settling being conducted at a temperature above that at which said low pour test oil can be obtained by centrifugal dewaxi ing; separating the bulk of the lubricating oil as a low pour test top layer from the wax settlings containing a substantial proportion of wax and separating the top oil from the wax settlings and dewaxing the latter by centrifugal force by means of a liquid separator.

HERSCHEL G. SMITH.

CERTIFICATE OF CORRECTION.

Patent No. 1,989,028. January 22, 1935.

HERSCHEL G. SMITH.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, second column, lines 44 and 45, claim l l, strike out the words "chilling and cold settling coagulant to such an oil,"; and lines 54 and 55, of said claim, strike out the words "separating the top oil from the wax ,settlings and"; and that the said Letters Patent should be. read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 12th day of March, A. D. 1935.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

